Lets look at how you are getting through the ball, what we see a lot of when people are pitching is that they add loft.

The butt of the club goes behind the club face and the ball just pops in the air.

So a nice simple drill here, what I want you to do is grip right down the club, lean it on your left side and as you make the swing work through and maintain that angle. You want the feeling that the butt of the club is going past your left pocket.